Acoustic drivers are often used in conjunction with sound-radiating horns in sound applications requiring high acoustic power output or sound volume, such as in theaters, arenas, or for studio and stage monitoring, and the like. In many sound systems, separate components such as driver and horn assemblies or conventional sound enclosure loudspeakers are used for sound reproduction across the entire range of audible sound, with different devices covering the bass, midrange and high frequency portions of the audible spectrum.
A particular sound application may require an especially high power output across the spectrum. With respect to the high frequency range, this has been attempted in the past in at least two different ways. A first attempt included an increase of the number of high frequency driver and horn assemblies. When multiple drivers are used, the output increases. For example, if four drivers are combined, the output power increases and causes an increase in perceived loudness. Thus, one could attempt to line up a series of high frequency drivers each connected to horn assemblies to provide the high-powered output. This solution, however, results in destructive interference and requires too large a space for many applications.
Second, it may be possible to use a system of multiple drivers coupled with a single horn. In particular, this would result in less bulk, lower weight, lower cost than having several sound sources operating at the same time. It is difficult, however, to properly combine multiple drivers with a single horn, especially when high frequencies are concerned. Ideally, the distance between the multiple drivers would be less than ⅓ the wavelength of the highest frequency to avoid sound wave interference. At high frequencies, the sound wavelength can be very small, therefore making it difficult to place the drivers at a distance less than the wavelength. For example, the approximate one-third wavelength at a frequency of 10 kHz is 0.44 inches. Given that drivers oftentimes have a diameter of approximately 4 inches or more, it would not be possible to put two or more drivers next to one another at less than 0.44 inches. In other words, any meaningful design of the horn enclosure would require the depth to be so large as to be impractical.
There have been various attempts to combine multiple acoustic drivers with a single horn. One attempt was to use a “Y” combiner. The “Y” combiner includes a “Y” shaped throat with a separate branch attached to each driver. Sound is generated by the acoustic drivers and flows down each separate branch and at meets at the combined throat portion. At high frequencies, however, the multiple sound waves meet together and may cancel each other out or create substantial interference.
Another attempt to combine multiple high frequency drivers with a single horn was to use an Electrovoice Manifold. The Electrovoice Manifold attempted to eliminate sound wave interference from multiple drivers by reflecting each sound wave at a reflecting surface so as to combine with the other sound waves with minimal interference. Reflection of sound waves, however, is largely unpractical in these circumstances. For proper reflection of a wave, the reflector must be large relative to the actual wavelength. In some examples, the reflector must be at least 20 wavelengths long to be effective. When dealing with high frequency of sound, wavelengths may range from ⅝ inch to a few inches, thus requiring very large reflectors. Oftentimes, it would be impractical to use such a large reflector.
It is also desirable to form a properly shaped wavefront to efficiently couple with the horn portion. When a plane wave from a relatively large source is coupled to a horn, the dimension of the source ends up controlling the high frequency radiation pattern rather than the more desirable outcome of the horn controlling the radiation pattern. It is therefore desirable to create a curved wavefront, such as one having the form of a segment of a sphere, rather than a flat wavefront to couple with the horn.
The Paraline system, described in U.S. Patent Publication 2009/0323997 to Danley discloses a method of combining the output of two or more acoustic drivers into one coherent output. The Paraline system, however, produces a wavefront that may not be optimal for coupling with the shape of the horn and can produce a curved wavefront only in a simple plane.
Accordingly, a sound reproduction system for efficiently combining sound output from multiple compression drivers with a horn mouth portion would be advantageous.